1. Field of the Invention
This invention relates generally to telecommunications, and more particularly, to wireless communications.
2. Description of the Related Art
In CDMA2000 standard Revision D, users of a plurality of wireless devices, such as a mobile station, either makes data transmissions on a reverse link autonomously, or based on schedule grants/rate control directives from a plurality of base station sectors. A schedule grant is a explicit communication to the mobile station from a base station indicating that it may transmit data up to a certain rate control command is a three-valued symbol (+1, 0 (no transmission),−1) that indicates to a single mobile or a group of mobiles that it may increase, shall hold or shall decrease its transmission rate by a known value he former type of rate control command is termed dedicated and the latter type is termed common. Absolute rate allocations as well as changes to rate allocations are equivalently specified as maximum traffic to pilot or (T/P) allocations. The traffic to pilot ratio specifies how much power the mobile station may use for the traffic (or data) channel relative to the power with which it is transmitting the pilot.
In a Revision D system, mobile stations transmit data on a traffic channel known as the reverse packet data channel (R-PDCH). Transmissions on the R-PDCH follow a retransmission protocol based on the receipt of positive or negative acknowledgements (ACK/NACK) feedback from the receiving base station sectors. Upon receipt of a negative acknowledgment, the mobile station retransmits the data until either a positive acknowledgement is received or the limit on retransmissions is reached. Typically, three attempts to transmit the same data are allowed. The unit of data that is being attempted to be transmitted is designated an encoder packet. The same unit of data when prepared for transmission over the air by encoding and modulating the bits is designated a sub-packet. Multiple sub-packets may be derived from the same encoder packet. At the base station, the sub-packets may be used singly or in combination with each other to recover the encoder packet.
Mobiles are said to be in handoff if they are in communication with more than one base station sector. The sectors that transmit and receive to the mobile are said to be members of the active set of sectors or the mobile's active set. One of these sectors is designated the serving sector and this sector is typically responsible for ensuring that the mobiles are given fair treatment in terms of permission to transmit as well as in the assignment of rates. Only the serving sector transmits a schedule grant. However all sectors may each transmit a rate control command and these are used at the non-serving sectors to ensure that the mobile's transmissions do not cause excessive interference.
A typical rule for rate control is that the mobile raised its transmission rate only if all the active set sectors send a rate UP command to it. It lowers its rate if any of the sectors transmits a DOWN command and HOLDS its rate otherwise. Two illustrative modes of operation are now described.
In Case 1, the mobile in the handoff zone is controlled by a common rate control protocol. At each sector, a single rate control command is transmitted to control the transmission rates of all mobiles that contain the sector in the active set. The serving sector wishes to raise the transmission rate of the mobile by a substantial amount and so sends a schedule grant to the mobile specifying a rate limit substantially higher than the rate to which the mobile is currently limited. Typically, the serving sector will transfer the high rate allocation from one mobile to the other to ensure fair treatment.) If any of the other sectors in the mobile's active set send a rate DOWN or a rate HOLD command at the same time, and the typical rule stated above is used by the mobile, it will not be able to raise its transmission rate. As a result, the serving sector has lost the ability to raise the rate of the mobile. Even if the non-serving sectors each transmit an UP at the same time as the grant, the mobile may raise its rate by at most one value (UP by one rate).
In Case 2, the mobile in the handoff zone is controlled by a dedicated rate control protocol. At each sector, separate and potentially different rate control commands are transmitted to control the transmission rates of this and other mobiles that contain the sector in their active set. The serving sector wishes to raise the rate of the mobile's transmission by sending a schedule grant. The same problems in Case 1 occur if the typical rule above is used by the mobile to determine its transmission rate. Further, the non-serving sectors must continuously transmit UP to each mobile to allow the mobile to raise its rate, whether a schedule grant or a rate control command is used at the serving sector to raise the mobile's transmission rate. If the non-serving sector stays silent, the mobile will be forced to HOLD its rate according to the typical voting rule specified above.
The present invention is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.